The present invention relates to a fuel feeding apparatus for an internal combustion engine and a vehicle using the fuel feeding apparatus, and especially, the invention relates to a fuel feeding apparatus which is effective to improve the characteristics of engine starting and to realize a stable fuel injection.
A fuel feeding apparatus for directly injecting fuel in cylinders of an internal combustion engine, typically referred to as a direct injection type fuel feeding apparatus, is able to feed an accurate amount of fuel to the cylinders of the engine, and has proven to be an effective means to improve the characteristics of engine starting. For a diesel engine, a direct injection type fuel feeding apparatus has been dominantly used, and also for a gasoline engine, the use of a direct injection type fuel feeding apparatus in place of an air-intake pipe injection type fuel feeding apparatus is becoming more common. Further, in an internal combustion engine using a direct injection type fuel feeding apparatus, the pressure of the fuel injection tends to further increase. The pressure of fuel injection in a direct injection gasoline engine is about 5-10 MPa, higher by 15 times than the pressure of fuel injection in an air-intake pipe injection type internal combustion engine. The requirement of a high pressure for a direct injection gasoline engine causes a problem in that the time necessary to increase the pressure of fuel injection to a preset high pressure value becomes elongated, which degrades the characteristics of engine starting.
To solve this problem, in a fuel feeding apparatus disclosed in JP-A-321787/1993, an auxiliary pump used exclusively to increase the fuel pressure at the time of engine starting is provided in addition to the ordinary high pressure fuel pump for pressurizing fuel to a high pressure value, which is continuously operated during operation of the internal combustion engine. The auxiliary pump is driven by fuel of low pressure, which is fed from a fuel feed pump, and serves to supplement the pressure which is increasing in a high pressure fuel system at the time of engine starting. After the engine has stopped, the operational state of the auxiliary pump is returned to its initial state, and the pressure of the fuel in the high pressure fuel system is decreased.
A fuel feeding apparatus for a direct injection gasoline engine is disclosed, for example, in JP-A-158536/1995 or JP-A-28335/1996. The fuel feeding apparatus disclosed in each of these documents comprises a low pressure fuel feed pump for pressurizing fuel to a low pressure and transferring the fuel of low pressure, a high pressure fuel pump, a low pressure regulator and a high pressure regulator for regulating the discharge pressure of each pump, fuel injection valves provided at respective cylinders of an engine, and fuel pipes connecting the above-mentioned components. In the following, the operations of these components will be explained.
The low pressure fuel feed pump is installed at or in the vicinity of a fuel tank provided at the back part of a vehicle, and this pump feeds gasoline in the tank to the engine compartment provided at the front part of the vehicle. The gasoline to be fed is first pressurized to about 0.3 MPa as controlled by the low pressure regulator. The high pressure fuel pump further pressurizes the gasoline of low pressure fed by the low pressure fuel feed pump to a high pressure and feeds it to the injection valves. The high pressure regulator regulates the pressure of the high pressure gasoline so as to keep a preset pressure value of 5-10 MPa. Then, each of the injection valves atomizes the high pressure gasoline, and directly injects the atomized gasoline into the respective engine cylinders.
Further, in a high pressure fuel pipe system, a means for removing vapor bubbles generated in the gasoline needs to be provided. That is, by providing the high pressure fuel pump at the beginning of the high pressure fuel pipe system and the high pressure regulator at the end of the high pressure fuel pipe system, gasoline including vapor bubbles generated in the fuel contained in the high pressure fuel pipe system is circulated between the high pressure fuel pump and the high pressure regulator, and the generated vapor bubbles are ejected from the gasoline by the high pressure regulator.
It is desirable to reduce the time necessary to increase the pressure of the fuel in a high pressure fuel system of a fuel feeding apparatus for a direct injection internal combustion engine to a preset high pressure value at the time of engine starting.
In the fuel feeding apparatus disclosed in JP-A-321787/1993, the time necessary to increase the pressure of the fuel in a high pressure fuel system (referred to as the fuel pressure increasing time) is reduced by the auxiliary pump provided for improving the engine starting. However, since the operational state of the auxiliary pump is returned to its initial state after engine is stopped, and the pressure of the high pressure fuel system is decreased, the process of increasing the pressure of the fuel in the high pressure fuel system from a low pressure state must be repeated every time the engine is started. Therefore, it is difficult to largely and efficiently reduce the fuel pressure increasing time by using the above-mentioned auxiliary pump.
Further, in order to improve the safety of the high pressure fuel system, it is desirable to reduce the length of each pipe set up in the high pressure fuel system by providing the high pressure regulator at a place as near as possible to the high pressure fuel pump, in each of which fluid of high pressure is processed. As mentioned above, since a method of circulating fuel between the high pressure fuel pump and the high pressure regulator is adopted to remove vapor bubbles in the gasoline in the conventional fuel feeding apparatus, the fuel feeding apparatus is arranged such that-the high pressure fuel pump is provided at the beginning of the high pressure fuel system and the high pressure regulator is provided at the end of the high pressure fuel system. Therefore, when the high pressure fuel pump and the high pressure regulator are installed near each other, the high pressure fuel pipe, in which the high pressure fuel flows and to which the injection valves are connected in order, is extended from the high pressure pump and is bent after the last injection valve. Further, the fuel-pipe is bent and connected to the high pressure regulator provided near to the high pressure fuel pump. In the above mentioned arrangement of the fuel feeding apparatus, the high pressure fuel pipe becomes undesirably long.
If the fuel pipe is long, it can cause an unstable performance problem in engine operations. That is, first the pressure of the fuel in the high pressure fuel pipe is decreased due to fuel injection from each injection valve, and then the pressure is adjusted and returned to the preset value by the high pressure regulator. Cycling of this decrease and increase in the pressure of the fuel in the high pressure fuel pipe is repeated. Due to this repeated cycling of the pressure of the fuel, the liquid fuel column in the high pressure fuel pipe is excited and oscillated. Since the period of fuel injection performed by the injection valves changes according to the engine speed, the frequency of the oscillating liquid fuel column also changes. If the characteristic frequency of the liquid fuel column in the high pressure fuel pipe is low, it is possible that the frequency of the excited oscillation at an ordinarily operating engine speed will coincide with the characteristic frequency of the liquid fuel column, so that a resonance phenomenon will be generated in the high pressure fuel pipe. In such a case, a large pulsation of the fuel pressure is caused, and the large pressure pulsation makes it impossible to accurately control the amount of fuel to be injected, which largely deteriorates the operational performance of the internal combustion engine.